1. The Field of Invention
This invention relates to an emergency breathing apparatus and, in particular, to an apparatus suitable for a sustained period of air supply useful for workers such as fire fighters in hostile areas.
2. Brief Statement of the Prior Art
Emergency breathing systems have evolved into a number of standardized versions. These include the devices for short periods of operation, e.g., about 5 minutes, and devices for sustained duration, typically 30 minutes. The latter have requirements such as remote pressure gauges to indicate to the user the pressure of the air supply bottle at all times, an audible alarm which is triggered when the air reservoir pressure falls below a predetermined value such as about 500 psig, and a demand face mask regulator which provides a flow of air to the user on demand. Typically, the air reservoir is a bottle at a high pressure, about 2000 psig and a pressure reducing valve is employed adjacent the face valve regulator to reduce the air pressure to about 80-100 psig. A flexible hose has been used to connect between the shut-off valve located at the air supply bottle and the pressure reducing valve. This flexible hose is a potentially hazardous structure since the hose can be ruptured or entangled during use of the device. In addition to this disadvantage, the prior systems have other drawbacks. The audible alarms used on prior devices have been operated by the air reservior pressure and have offered a compromise performance since the intensity of their alarm declines with the declining air reservior pressure. The mask regulator valves employed with the prior devices are relatively bulky and complex with a large number of moving parts which are prone to mechanical failure. Finally, the users commonly don the face mask with the air supply valve open and a significant amount of air is lost during the mask donning procedure.